This invention is related to the field of cell culture development systems. In particular, the invention is directed to a mixing apparatus and method which allows for the movement of cells in a liquid culture media both vertically and horizontally at a controlled rate, permitting adequate agitation and aeration of the culture media without damaging the cells. Further, the invention is directed to a lid design which creates a tight seal on various sized openings.
In various scientific fields, it is useful to grow cells in a culture media (such as a liquid suspension) over an extended period of time. However, increasing cell numbers results in the depletion of nutrients in the culture medium. When the media is allowed to stagnate, cell growth is inhibited and the cells can die. Any mixing device introduced to the culture media must be carefully selected and operated such that it does not damage the cells either by contaminating the culture media or by physically traumatizing the cells. Such a device must provide sufficient mixing such that nutrients are made available to most cells in the medium. Although innumerable mixing devices are known in other, unrelated and non-pertinent fields, they cannot be readily used or adapted to agitate cell cultures because they may create substantial stresses on the culture media, risking damage to the cells.
To overcome these problems, flasks have been developed which work in cooperation with stirring rods (or "spinners") to agitate the culture media and the cells. Typically, paddles are attached to the stirring rods, and are turned relatively slowly in the cultural media (about 5-150 rpm). While meeting with limited success, these devices generally fail to adequately agitate the cells. In particular, "dead spots" are created in the flasks in which portions of the liquid culture media are permitted to lie stagnant. These dead spots are most common along the sides and the bottom of the flask. Further, the flow created by these devices is generally laminar, both in horizontal bands and in vertical bands extending from the central axis outwardly. Consequently, the culture media and the cells are effectively mixed only in limited batches. It is often important for the cells and the cultural media to be exposed to the air. Since there is little vertical mixing, only the top most material in the flask is exposed to the air.
U.S. Pat. No. 3,622,129 is directed to a magnetic stirrer apparatus. A shaft extends through the bore of a closure in sealing relation therewith. A magnetic stirrer bar having a cylindrical shape is rotatably coupled to the shaft. The stirrer bar is pivoted on the shaft distal to the closure. Alternatively, the shaft and stirrer bar can be pivoted on the closure. A longitudinal adjustment of the shaft in the closure provides that the apparatus can be used with flasks of various sizes. The shaft and the stirrer bar are wholly encapsulated in a chemically inert plastic material, thereby avoiding contamination of the stirred matter. An external magnet magnetically engages the stirrer bar and causes it to rotate within the container. This results in a mixing of the material contained therein.
U.S. Pat. No. 4,355,906 is directed to a stirring apparatus for cell cultures. Substantially square blades with rounded corners are pivotally mounted to a central stirring assembly. A magnetic bar is also mounted to the stirring assembly. In operation, external magnets are rotated, thereby causing the magnetic bar mounted to the stirrer to rotate. The movement of the magnets on the stirrer causes the blades to rotate within the container and thereby causes the cell culture to be mixed.
U.S. Pat. No. 3,245,665 is directed to a magnetic mixing bar. The bottom of the bar is curved to approximate the shape of the bottom of the flask. Two magnetized rods are disposed in a bar. A rotating external magnet causes the bars in the rod to rotate. The use of two separate rods prevents the mixing bar from reversing polarity with the external magnet.
These references do not adequately address the problems solved by the instant invention, as one skilled in the art will appreciate from the following disclosure.